1. Field of the Invention
The present invention relates to a control device for a parallel type hybrid vehicle having an engine with deactivatable cylinders, and in particular, relates to a control device for a hybrid vehicle, which enables an improvement in fuel consumption while maintaining brake performance.
2. Description of the Related Art
A hybrid vehicle having not only an engine but also an electric motor as the drive source has been known in the art. As a type of hybrid vehicle, a parallel hybrid vehicle is known that uses an electric motor as an auxiliary drive source for assisting the engine output.
In the parallel hybrid vehicle, the power of the engine is assisted by the electric motor during acceleration traveling. On the other hand, during deceleration traveling, the battery and the like are charged via a deceleration regenerating operation. According to various control operations including the above, the remaining battery charge (remaining electric energy) of the battery is maintained while also satisfying the driver's demands. Because the drive train of the parallel hybrid vehicle comprises the engine and the motor coupled to the engine in series, the whole system is simple in structure, light in weight, and has great flexibility for installation in the vehicle.
As variations of the parallel hybrid vehicle, two types of hybrid vehicles are known; one is disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. 2000-97068, in which a clutch is disposed between the engine and the motor in order to eliminate the effect of engine friction (i.e., engine brake) during the deceleration regenerating operation; the other is disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. 2000-125405, in which the engine, the motor, and a transmission are directly connected in series in order to ultimately simplify the structure.
The hybrid vehicle of the former type exhibits disadvantages in that the installability of the power train is degraded due to the complexity in the constitution of the clutch, and the transmission efficiency of the power train may be reduced during normal traveling as well due to the use of the clutch. On the other hand, the hybrid vehicle of the latter type exhibits a disadvantage in that the driving power assisted by the electric motor (assisted power) is restricted because regenerated electric energy is reduced due to the aforementioned engine friction.
As another measure to reduce the engine friction during deceleration, an electronic control throttle mechanism may be used which controls a throttle valve to be open during deceleration so as to greatly reduce the pumping loss and to increase the regenerative energy; however, a considerable amount of new air directly flows into the exhaust system during deceleration, which may lower the temperature of a catalyst and an air flow sensor and could cause inappropriate exhaust gas control.
A cylinder deactivation technique has been proposed to solve the above problem; however, the cylinder deactivation period is limited in order to retain a sufficient negative pressure in the master vac for the brake system, and consequently, not much regenerative energy can be saved by the reduction of engine friction.